/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.tomcat.util.threads;

import java.util.Collection;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.TimeUnit;

/**
 * As task queue specifically designed to run with a thread pool executor.
 * The task queue is optimised to properly utilize threads within
 * a thread pool executor. If you use a normal queue, the executor will spawn threads
 * when there are idle threads and you wont be able to force items unto the queue itself
 *
 * @author fhanik
 */
public class TaskQueue extends LinkedBlockingQueue<Runnable> {

	private static final long serialVersionUID = 1L;

	private ThreadPoolExecutor parent = null;

	// no need to be volatile, the one times when we change and read it occur in
	// a single thread (the one that did stop a context and fired listeners)
	private Integer forcedRemainingCapacity = null;

	public TaskQueue() {
		super();
	}

	public TaskQueue(int capacity) {
		super(capacity);
	}

	public TaskQueue(Collection<? extends Runnable> c) {
		super(c);
	}

	public void setParent(ThreadPoolExecutor tp) {
		parent = tp;
	}

	public boolean force(Runnable o) {
		if (parent.isShutdown())
			throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
		return super.offer(o); //forces the item onto the queue, to be used if the task is rejected
	}

	public boolean force(Runnable o, long timeout, TimeUnit unit) throws InterruptedException {
		if (parent.isShutdown())
			throw new RejectedExecutionException("Executor not running, can't force a command into the queue");
		return super.offer(o, timeout, unit); //forces the item onto the queue, to be used if the task is rejected
	}

	@Override
	public boolean offer(Runnable o) {
		//we can't do any checks
		if (parent == null) return super.offer(o);
		//we are maxed out on threads, simply queue the object
		if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
		//we have idle threads, just add it to the queue
		if (parent.getSubmittedCount() < (parent.getPoolSize())) return super.offer(o);
		//if we have less threads than maximum force creation of a new thread
		if (parent.getPoolSize() < parent.getMaximumPoolSize()) return false;
		//if we reached here, we need to add it to the queue
		return super.offer(o);
	}

	@Override
	public Runnable poll(long timeout, TimeUnit unit)
			throws InterruptedException {
		Runnable runnable = super.poll(timeout, unit);
		if (runnable == null && parent != null) {
			// the poll timed out, it gives an opportunity to stop the current
			// thread if needed to avoid memory leaks.
			parent.stopCurrentThreadIfNeeded();
		}
		return runnable;
	}

	@Override
	public Runnable take() throws InterruptedException {
		if (parent != null && parent.currentThreadShouldBeStopped()) {
			return poll(parent.getKeepAliveTime(TimeUnit.MILLISECONDS),
					TimeUnit.MILLISECONDS);
			// yes, this may return null (in case of timeout) which normally
			// does not occur with take()
			// but the ThreadPoolExecutor implementation allows this
		}
		return super.take();
	}

	@Override
	public int remainingCapacity() {
		if (forcedRemainingCapacity != null) {
			// ThreadPoolExecutor.setCorePoolSize checks that
			// remainingCapacity==0 to allow to interrupt idle threads
			// I don't see why, but this hack allows to conform to this
			// "requirement"
			return forcedRemainingCapacity.intValue();
		}
		return super.remainingCapacity();
	}

	public void setForcedRemainingCapacity(Integer forcedRemainingCapacity) {
		this.forcedRemainingCapacity = forcedRemainingCapacity;
	}

}
